Carbon allotropes encompass 0-D fullerenes, 1-D nanotubes, 2-D graphenes, and 3-D graphite and diamond, among which graphenes are of particular interests due to their unique features. The 2-D graphenes are one-atom thick nanosheet composed of hexagonal structure of carbon atoms, giving rise to exceptional electrical conductivity (8×105 S/m), high thermal conductivity (about 5300 W m−1 K−1), large surface areas (>2600 m2/g), strong mechanical properties (tensile strength of 130 GPa and Young's modulus of 1 TPa), low friction coefficient and excellent corrosion resistance.
The possible low-cost production of graphenes from graphite via oxidation-intercalation, exfoliation and reduction processes makes it an attractive conductor for many purposes. High-degree dispersion of graphenes in the polymer matrix can be realized, but it is not accessible for ceramics, glass, metals and semi-conductor materials because they are processed at temperatures above 400° C., at which graphenes are not thermally stable. Therefore, it is of particular importance to coat the surfaces of those solids with a thin layer of graphene to gain many, if not all, of its advantages.
Since the graphene surface is very inert, individual graphene layers can be easily peeled off from a multi-layer stack and direct coating of graphene layers on the surface of solids requires the use of adhesives, which often cannot withstand high temperatures. Furthermore, the presence of adhesives may reduce the graphene properties.
In the present invention, we describe a novel approach to coat the solid surfaces with graphene-like network at elevated temperatures, during which graphene-like structure is formed from chemical vapor deposition of solid, liquid or gas carbon sources and deposited on the surface of solid substrates. In the presence of silicon, metal and sometimes a small amount of oxygen, the edge carbon atoms of graphene-like structure may form covalent bonds such as (—C—O—Si—), (—C—Si—), (—C—O-M-) and/or (—C-M-) among themselves and with the silicon and/or metal atoms in the ceramics, glass, quartz, silicone wafer and metals. Because of this, the coated graphene-like network has strong bonding among graphene-like structures and with the solid substrates, which can withstand high stresses and high temperatures even in the air. This graphene-like network coating endows the solids with unique properties, allowing them to prospect as an attractive material for a variety of potential applications.
As an example, the vast majority of useful ceramics, glass and quartz are electrical and thermal insulators. To make their surfaces electrically and thermally conductive, a coating layer comprised of a dispersion of noble metal powders, e.g., platinum, gold, or silver, to give the electrical conductivity in the order of 1,000 S/m is often applied. In spite of high cost, noble metals are still used to a great extent because non-noble metal powders such as copper, nickel, or aluminum, are easy to form high resistance surface oxides. The expense of noble metals and the disadvantages of using non-noble metal powders have prompted researchers to search for alternative approaches. The present invention of covalently-bonded graphene coating serves as an excellent solution.
In light of their high electrical and thermal conductivity, high mechanical strength, excellent resistance to acid and base, low friction, high hydrophobicity, tunable semi-conductive and optical properties, and strong bonding among graphene-like structures and between graphene-like structures and ceramics, glass and quartz, the covalently-bonded graphene-like network coating of ceramics, glass and quartz can find many applications. For example, the current collector of the energy conversion devices is often exposed to an extremely corrosive environment. Because of the severe corrosion problems, many metals are not practical for such use. The covalently-bonded graphene-like network coating of ceramics, glass and quartz are a promising alternative.
Another example is the application for heat-dissipation systems of microelectronic packaging. As the speed of processor increases, the generated heat would dramatically increase. Thus, the application of high thermal conductivity materials is essential to thermal management in compact packaging systems. Since graphene has a very high thermal conductivity, the graphene-like network coated solids may be used there.
Because graphene has a very low friction coefficient, the covalently-bonded graphene-like network coating of solids can be used as ball bearing and for many friction and binding reduction applications. A combination of high thermal conductivity, desirable electric conductivity/resistivity and low binding surface makes the covalently-bonded graphene-like network coating of ceramics, glass and quartz an excellent candidate for energy saving and non-sticking cooking ware.
Yuegang Zhang et al disclosed a method for deposition of graphene on various dielectric substrates in Nano Lett. 2010, 10, 1542-1548. A single-layer graphene is formed through surface catalytic decomposition of hydrocarbon precursors on thin copper films pre-deposited on dielectric substrates. The copper films de-wet and evaporate during or immediately after graphene growth, resulting in graphene deposition directly on the bare dielectric substrates. However, copper is applied in the process.
US 20110070146 A1 disclosed a method of manufacturing graphene, a graphene comprising a base member, a hydrophilic oxide layer formed on the base member, and a hydrophobic metal catalyst layer formed on the oxide layer. The graphene grown on the metal catalyst layer and then apply water to the graphene member. At a final step, the metal catalyst layer is separated from the oxide layer to obtain the graphene. In the method, an etching process is required to remove the metal catalyst layer.